警告：内建函数“XYZ”不兼容的隐式声明 [英] warning: incompatible implicit declaration of built-in function ‘xyz’

问题描述

我编译了一些二进制文件时，取得了一些这些警告：

I'm getting a number of these warnings when compiling a few binaries:

warning: incompatible implicit declaration of built-in function ‘strcpy’
warning: incompatible implicit declaration of built-in function ‘strlen’
warning: incompatible implicit declaration of built-in function ‘exit’

要设法解决这个问题，我已经添加了

To try to resolve this, I have added

#include <stdlib.h>

在此警告相关的C文件​​的顶部，除了与以下标志编译：

at the top of the C files associated with this warning, in addition to compiling with the following flags:

CFLAGS = -fno-builtin-exit -fno-builtin-strcat -fno-builtin-strncat -fno-builtin-strcpy -fno-builtin-strlen -fno-builtin-calloc

我使用GCC 4.1.2：

I am using GCC 4.1.2:

$ gcc --version
gcc (GCC) 4.1.2 20080704

我应该怎么做来解决这些警告？

What should I do to resolve these warnings?

推荐答案

在C，使用previously未声明的函数构成了功能的隐式声明。在一个隐含的声明中，返回类型是 INT 如果我没有记错。现在，GCC还内置了一些标准函数的定义。如果一个隐含的声明不匹配内置的定义，你得到这样的警告。

In C, using a previously undeclared function constitutes an implicit declaration of the function. In an implicit declaration, the return type is int if I recall correctly. Now, GCC has built-in definitions for some standard functions. If an implicit declaration does not match the built-in definition, you get this warning.

要解决这个问题，必须在使用前声明函数;通常您可以通过包括适当的头做到这一点。我不建议如果可能的话使用-fno-builtin- *标志。

To fix the problem, you have to declare the functions before using them; normally you do this by including the appropriate header. I recommend not to use the -fno-builtin-* flags if possible.

相反stdlib.h中，你应该尝试

Instead of stdlib.h, you should try

#include <string.h>

这就是的strcpy 和函数strncpy 定义，至少根据的strcpy（2）手册页。

That's where strcpy and strncpy are defined, at least according to the strcpy(2) man page.

的退出函数是在stdlib.h中定义，虽然如此，我不知道发生了什么事情在那里。

The exit function is defined in stdlib.h, though, so I don't know what's going on there.

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